1. Field of the Invention
The present invention relates to methods and materials for high speed radiation-induced functionalizing of substrates, and more particularly to methods and materials for functionalizing substrates by selectively transforming surface-bound chemisorbed functional groups with high photospeeds. This transformation is accomplished by exposing the functionalized substrates to actinic radiation and then further reacting the substrates by carrying out substitution (grafting) reactions to impart a desired characteristic to the substrate.
2. Description of the Related Art
Selectively modified substrates are useful in a variety of applications, including microelectronics, lithography, optics, and medical technology. Of particular interest is the selective modification of substrates such as silicon, silica, plastics, metals, metal oxides, and ceramics. In particular, selective deposition of adherent, conductive metal coatings on these substrates is of great technological interest for high resolution integrated circuit fabrication and printed circuit applications. The use of patterned irradiation in selectively modifying these substrates is a useful technique, due to the ability of this technique to spatially control modification placement, and due to the high resolution that can be achieved.
Typically in these processes, a substrate is modified by the attachment of chemical functional groups. The chemically modified surface is then exposed to patterned actinic radiation, such as through a mask, thereby altering the chemical nature of selected areas on the surface. In this context, actinic radiation is any radiation that can effect the desired change in the chemical nature of the surface, such as visible or ultraviolet light, x-rays, .gamma.-rays, ions, electron beams, etc.
Typically, after the surface has been irradiated, further processing steps are employed, depending on the particular application at hand. For example, in metallization applications the attached chemical functional groups are ligands and these ligands are deactivated or transformed by actinic radiation. Ligands are defined herein to be chemical moieties capable of complexing with catalysts for electroless metallization. After irradiation these surfaces are catalyzed, then selectively metallized by immersion in an electroless metallization plating bath. See, e.g.. U.S. patent application Ser. No. 07/933,147, filed Aug. 21, 1992 by Calvert, Pehrsson and Peckerar, which is incorporated by reference herein. See also co-pending application Ser. No. 07/691,565.
A problem with many of these processes is that typically the exposure step has a very low irradiative efficiency, or photospeed. In this context, photospeed is inversely related to the amount, i.e. fluence, of actinic radiation (typically measured in mJ/cm.sup.2 for photons, ions/cm.sup.2 for ions, or .mu.A/cm.sup.2 for electrons) required to effect the necessary change in the chemical nature of the surface. For example, when pyridyl groups in films of 2-(trimethoxysilyl)ethyl-2-pyridine are attached to an SiO.sub.2 substrate, the irradiative conversion of these groups to a non-binding photo-product requires about 1500 mJ/cm.sup.2 of deep UV (193 nm) radiation. The drawbacks to such low photospeeds include longer exposure times, larger energy requirements, and decreased likelihood of the photoreaction resulting in the desired photoproducts.